1. Field of the Invention
The present invention relates to a method and apparatus for supporting a patient, particularly while reducing the patient interface pressures (i.e. the pressures exerted against the patient's skin) in a manner which reduces the likelihood of bed sores and other complications. More particularly, it relates to a patient support having a plurality of inflatable air bags in combination with means for rotating a supported patient first in one direction and then back in the opposite direction in order to help prevent complications of prolonged immobility. The invention also relates to control systems for controlling such a bed.
2. Background References
Other devices are known which are directed to the same object, but these devices are limited in several respects. In particular, U.S. Pat. No. 3,822,425 discloses an air mattress consisting of a number of cells or bags, each having a surface which supports the patient formed from a material which is gas permeable but is non-permeable to liquids and solids. It also discloses an air supply for inflating the cells to the required pressure and outlets or exhaust ports to allow the escape of air. The stated purpose of the outlets is to remove condensed vapor for the cells or bags. The outlets on that mattress may be fitted with valves to regulate the air pressure in the cells as opposed to regulating the air pressure in the cells by controlling the amount of air flowing into the cells. However, the air bed which is described in that patent and which is currently being marketed under that patent is believed to have certain disadvantages and limitations.
For example, that bed has a single air intake coupler, located directly and centrally underneath the air mattress, for connection of the source of air. Access to this connection is difficult since one must be on their back to reach it. The location of the connection underneath the mattress creates a limitation in the frame construction because the air hose must pass between the bed frame members. The source of air to which the air hose is connected is a blower or air pump mounted in a remote cabinet which, because it must be portable, is mounted on casters. There are many times in actual use when the cabinet must be moved in order to wheel other equipment, such as I.V. stands, around it or for access to the patient. However, relocation of this blower unit by any significant distance requires disconnection of the air hose from the frame (inconvenient because of the location up underneath the frame) or the pendant control in order to avoid wrapping the air hose around the bed frame members. Of course, disconnection of the air hose results in the loss of air pressure in the air mattress, which is even less desirable.
Further, the bed disclosed by that patent is limited in that only a finite amount of air can be forced or pumped into the air mattress. By eliminating the outlets described in that patent entirely, the air pressure in the bags can at least be maintained at that point which represents the maximum output of the source of gas. In the case of the bed described in that patent, if it is necessary to further increase the pressure in the air bags while the outlets are being used for their stated purpose, the only way to do so is to install a larger capacity blower in the cabinet. High air pressures may be necessary, for instance, to support obese patients. A larger capacity blower generally requires more power consumption and a higher capacity circuit which may not be readily available. Also, the larger the blower, the more noise it creates which is not desirable.
Another limitation of that bed is the necessity for constant adjustment of the air pressure in the air bags on which the patient is supported. Although low air loss beds in general are used for bedridden patients, not all bedridden patients are incapable of movement. Each movement of those patients, even such movements as moving only one arm, or each time a patient incapable of movement is re-positioned by attending health-care personnel, causes changes in the portion of the patient's weight supported by the sets of air bags mounted on the respective head, back, seat and leg sections of the frame of the bed. To avoid the localized increases in the pressure exerted against the skin of the patient as a result of such movements, the air pressure in that section must be re-adjusted. Adjustment of the air supply to one set of air bags almost invariably has an effect on the pressure in one or more adjacent sets of air bags such that it is often necessary to change the air supply to every set of air bags on the bed.
Further, low air loss beds of the type disclosed in the '425 patent are provided with means for adjusting the patient's attitude on the bed. For instance, the head of the bed can be raised to sit the patient up or the angle of the entire frame of the bed can be changed with respect to the horizontal when, for therapeutic reasons, the patient is placed in the Trendelenburg or reverse Trendelenburg positions. Those changes requirereadjustment of the air supply in each set of air bags, usually of a greater magnitude than those required as a result of the movement of the patient.
The limitations and disadvantages which characterize other previous attempts to solve the problem of preventing bed sores in bedridden patients are well characterized in British Patent. No. 1,474,018 and U.S. Pat. No. 4,425,676.
Other references also disclose a number of devices which function to rock a patient back and forth by the use of air pressure. For instance, U.S. Pat. Nos. 3,477,071, 3,485,240, and 3,775,781 disclose hospital beds with an inflatable device for shifting or turning a patient lying on the bed by alternately inflating and deflating one or more inflatable cushions. U.K. Patent Application No. 2,026,315 discloses a pad, cushion, or mattress of similar construction. German Patent DE 28 16 642 discloses an air mattress for a bedridden person or hospital patient consisting of three longitudinal inflatable cells attached to a base sheet, the amount of air forced into each cell being varied so as to alternately rock the patient from one side of the mattress to the other. However, none of those mattresses or devices are designed for use in a low air loss patient support system. Further, the U.K. and German patents, and U.S. Pat. Nos. 3,477,071 and 3,775,781, disclose devices consisting of parallel air compartments which extend longitudinally along the bed and which are alternately inflated and deflated. Such a construction does not allow the use of the device on a bed having hinged sections corresponding to the parts of the patient's body lying on the bed so that the inclination and angle of the various portions of the bed can be adjusted for the patient's comfort.
U.S. Pat. No. 3,678,520 discloses an air cell for use in a pressure pad which is provided within a plurality of tubes which project from a header pipe such that the air cell assumes a comb-like confirmation when inflated and viewed from above. Two such air cells are enclosed within the pressure pad with the projecting tubes interdigitating, and air is alternately provided and exhausted from one cell and then the other. That device is not suitable for use on a bed having hinged sections corresponding to the parts of the patient's body lying on the bed so that the angle of inclination of the various portions of the bed can be adjusted for the patient's comfort, nor is it capable of functioning in the manner described if constructed in the low air loss conformation.
A number of patents, both U.S. and foreign, disclose air mattresses or cushions comprised of sets of cells which are alternately inflated and deflated to support a patient first on one group of air cells and then the other group. Those patents include the following U.S. Pat. Nos.: 1,772,310, 2,245,909, 2,998,817, 3,390,674, 3,467,081, 3,587,568, 3,653,083, 4,068,334, 4,175,297, 4,193,149, 4,197,837, 4,225,989, 4,347,633, 4,391,009, and 4,472,847, and the following foreign patents: G.B. 959,103, Australia 401,767, and German 24 46 935, 29 19 438 and 28 07 038. None of the devices disclosed in those patents rocks or alternately moves the patient supported thereon to further distribute the patient's body weight over additional air cushions or cells or to alternately relieve the pressure under portions of the patient's body.
There are also a number of patents which disclose an inflatable device other than an air mattress or cushion but which also involves alternately supplying air to a set of cells and then to another set of cells. Those patents include U.S. Pat. Nos. 1,147,560, 3,595,223, and 3,867,732, and G.B. Pat. No. 1,405,333. Of those patents, only the British patent discloses the movement of the body with changes in air pressure in the cells of the device. None of those references disclose an apparatus which is adaptable for use in a low air loss patient support system.
British Pat. No. 946,831 discloses an air mattress having inflatable elongated bags which are placed side-by-side and which are in fluid communication with each other. A valve is provided in the conduit connecting the insides of the two bags. Air is supplied to both bags in an amount sufficient to support the patient, thereby raising the patient off the bed or other surface on which the air mattress rests. Any imbalance of the weight distribution of the patient causes the air to be driven from one bag to the other, allowing the patient to turn toward the direction of the now deflated bag. An automatic changeover valve, the details of which are not shown, is said to then inflate the deflated bag while deflating the bag which was originally inflated, thereby rocking the patient in the other direction. That device is limited in its ability to prevent bed sores because when the patient rocks onto the deflated bag, there is insufficient air to support the patient up off the bed or other surface on which the air mattress rests, resulting in pressure being exerted against the patient's skin which is essentially the same as the pressure that would have been exerted by the board or other surface without the air mattress. Even if there were enough air left in the deflated bag to support the patient, if the air mattress were constructed in a low air loss configuration, the air remaining in the bag would be slowly lost from the bag until the patient rested directly on the bed or other surface with the same result. Finally, that device is not adaptable for use on a bed having hinged sections corresponding to the parts of the patient's body lying on the bed so that the angle of inclination of the various portions of the bed can be adjusted for the patient's comfort.
European Patent Application No. 0,122,666 (published Oct. 24, 1984 and listing Maarten Swart as inventor) discloses a lying-down patient support including an air supply system having a pressure sensor for sensing the pressure in a feed duct common to each of its air cushions. The pressure sensor is tapped into the common feed duct upstream of the valves for controlling inflation of the air cushions. If the pressures are to be measured in one of its lifting bellows or in one of its air cushions, some of the valves are closed, and a computer obtains the pressure information from the pressure sensor. If the pressure has to be raised in one of the lifting bellows or in one of the air cushions, air constantly maintained at 1 to 2 atm. is then provided through those valves which remain open. By a regular check of the pressure in each cushion or a group of cushions, the control of the valve may take place fully automatically so that at any instant the pressure can be maintained.
European Patent Application No. 0,168,213 (published Jan. 15, 1986 and listing Evans as inventor) purports to disclose a feedback-controlled air support system. The disclosed unit purportedly operates to control the supply of air to and from sets A and B sequentially and alternately during what is referred to as a "dumb cycle" so that one set is vented and the other set inflated until preset sensing pressure level and support pressure levels are obtained and held. Possibly after a delay, the processor unit purportedly reverses the operation so that portions of the pad or mattress providing support are continually changed. Similarly, a change-over valve 24 is included to purportedly "connect the pressure sensor 25 alternately with both sets of cells at a rate controlled by the control section 10." (Pages 12-13). The disclosure also describes an "initialisation procedure" of the system which adjusts automatically the operating air pressure of the sets in accordance with an individual's body weight and, purportedly, posture and comfort (see pages 18 and 19 of its specification).